Regulations related to renewable fuels provide an example of how product requirements can change over time. The United States, Canada, and the European Union have recently increased and/or are likely to increase the required amount of product from renewable sources that is contained in transportation fuels. Based on such regulatory requirements, fuels from vegetable, animal, or algae sources such as “biodiesel” will become increasingly important as a refinery product. As a result, methods are needed that will allow existing refinery equipment to produce suitable transportation fuels that incorporate increasing amounts of renewable components.
Unfortunately, the differences in chemical composition between renewable carbon sources and mineral sources pose some difficulties for refinery processing. For example, typical biologically-derived sources for fuels have oxygen contents of 1 wt % or more, possibly as much as 10 wt % or more. Conventional hydroprocessing methods can remove oxygen from a feedstock, but the by-products from deoxygenation can lead to catalyst poisoning and/or contaminant build-up in a reaction system.
One potential feedstock source for making renewable diesel products is to use a feedstock that contains triglycerides. Triglycerides are present in many typical sources used as feedstock for making renewable products. Typical triglycerides useful for making renewable products include a three carbon glycerol backbone that has ester linkages to three longer side chains. Separating the side chains from the glycerol backbone typically results in formation of a fatty acid corresponding to each of the side chains. After separation from the glycerol backbone, the fatty acids can have a chain length that is suitable for use, possibly after further processing, in diesel products such as diesel fuels or diesel fuel additives.
U.S. Patent Application Publication 2010/0163458 describes a method for converting effluents of renewable origin into fuel. The method includes the use of a supported catalyst containing MoS2 and a dopant, such as phosphorus, carbon, or silicon. The method is described as favoring removal of oxygen by hydrodeoxygenation as opposed decarbonylation or decarboxylation.
U.S. Patent Application Publication 2011/0166396 describes a hydrodeoxygenation catalyst and a method for using such a catalyst. The catalyst is a supported catalyst containing Mo, with a support that includes a bimodal pore distribution. Additionally, at least 2 volume percent of the pores in the support are greater than 50 nm in diameter. The Mo catalyst with the specified pore distribution is used to perform hydrodeoxygenation on feeds containing up to 35 vol. % of renewable organic material.
U.S. Pat. No. 7,795,484 describes a process for the manufacture of base oil. The process includes converting fatty acids into alpha olefins via first an ester and then an alcohol intermediate. The alpha olefins are then used to form oligomers in the form of branched hydrocarbons that are suitable for use as a base oil. The resulting oligomers are then saturated to eliminate remaining olefins.
U.S. Pat. No. 7,888,542 describes a process for producing a saturated hydrocarbon component. Potential feeds for the process include feeds containing at least 50% by weight of compounds that are unsaturated or polyunsaturated. Triglycerides are noted as a potential type of compound that can be unsaturated. The initial process step is described as an oligomerization step, where carbon-carbon double bonds from two unsaturated compounds are reacted to form a single molecule. When a triglyceride is used as the source of unsaturated molecules, the triglyceride is first converted to another form before oligomerization. This can correspond to performing transesterification of the triglyceride in methanol to form FAME compounds, or it can correspond to exposing the triglyceride feed to a clay containing an alkali or alkaline earth metal, such as montmorillonite, that converts triglycerides and forms oligomers in a single catalyst bed. The oligomerized feed is then exposed to an (optional) pre-hydrogenation step where the oligomerized feed is treated with hydrogen in the presence of a supported Group VIII or Group VI/Group VIII catalyst. The pre-hydrogenation conditions are described as being effective for saturating double bonds and reducing formation of coke in subsequent steps. The hydrogenated, oligomerized feed is then deoxygenated in the presence another supported Group VIII or Group VI/Group VIII catalyst. Pd supported on alumina is noted as a preferred catalyst for a deoxygenation process that does not use hydrogen, while a sulfurized NiMo catalyst is noted as preferred for a deoxygenation process in the presence of hydrogen. In an embodiment where the feed contains carboxylic acids or carboxylic acid esters, it is noted that the deoxygenation step can be performed prior to the oligomerization. After deoxygenation, the resulting product can optionally be isomerized.